The present invention relates to improvements in lighting systems, in particular lighting systems having variable colour temperature.
Lighting systems having variable colour temperature are known in the art for improved comfort in office and domestic situations, and typically incandescent bulbs used in the evening have a lower colour temperature than the fluorescent lamps more commonly used during the day. The Solux Lamp (www.soluxtli.com) is a ‘cool’ light bulb, using a special coating, to emit light having a colour temperature of around 4700K. However, when dimmed this light source appears too blue at low light intensities, and for improved effectiveness of treatment and comfort a multiple light source approach is preferred.
Background prior art may be found in WO 96/28956, JP 05-121176, JP 04-206391, DE 3526590, JP 03-226903, EP 0545474, DE 3916997, U.S. Pat. No. 3,180,978, FR 2151121 and WO 85/01566. However, one problem with systems in the prior art is that they require new control wiring, extra mountings for light sources of different colour temperatures and sometimes special control means such as light sensors mounted on the outside of houses. Typically, prior art systems require at least two separate lighting circuits for controlling light sources of different colour temperatures, making them incompatible with standard domestic lighting installations and increasing the cost of providing artificial illumination with a variable colour temperature.
It would be advantageous to provide a lighting system with variable colour temperature capability which could be used with standard office and domestic lighting circuits, including standard light dimmers. In particular, it would be advantageous to provide a plug-in replacement for existing light bulbs, incorporating a variable colour temperature facility for use with existing light dimmer circuits.